Hispanic women in the Southwest and West have had lower breast cancer occurrence compared with non-Hispanic white women. However, in NM, incidence and mortality rates spanning the late 1950s through the late 1980s document rapidly increasing breast cancer occurrence in Hispanic women. Little information is available on risk factors for breast cancer in Hispanics; neither the low-risk status nor the increasing rates have been investigated. We propose to conduct complementary population-based investigations to 1) assess risk factors for breast cancer in Hispanic and non-Hispanic white women; 2) describe changes in risk factor distributions across birth cohorts of Hispanic women; 3) test for an effect of Hispanic ethnicity on breast cancer risk, after controlling for established breast cancer risk factors; 4) assess the prevalence of benign breast lesions in autopsy specimens accrued between 1992 and 1994 and compare the findings with similar data collected between 1978 and 1983; and 5) establish a resource of malignant and benign breast cancer tissues for future molecular and cellular studies. To accomplish these specific aims, we propose to: 1. Conduct a population-based case-control study in 400 Hispanic and 400 non-Hispanic white NM women with incident breast cancer and with equal numbers of controls. Risk factors to be considered include established risk factors related to reproduction, family history, benign breast lesions, radiation, and personal history of cancer. The case- control study will also test for effects of factors for which current evidence is less consistent or controversial: diet, including dietary nutrient intake, obesity and body size, use of oral contraceptives and postmenopausal estrogens, alcohol consumption, and lactation. Acculturation will be assessed in the Hispanic women and risk factor distributions examined in relation to acculturation status. 2. Conduct an autopsy study of benign breast lesions in 300 Hispanic and non-Hispanic women, including American Indians, with tissues available through the NM Office of the Medical Investigator, 1992-1994. The prevalence of proliferative and non-proliferative lesions will be compared with the findings of a similar study conducted between 1978 and 1983. 3. Develop a bank of malignant and nonmalignant breast tissue for future studies collected at surgery and autopsy from Hispanic and non- Hispanic women, including American Indians, having surgery at Albuquerque hospitals.